An enhancement function for improving image quality of a display video in a video display device has been known. With the enhancement function, stretch processing for expanding distribution of intensity of an input video signal is performed. For example, in the case of executing the enhancement function, typically, a maximum value of a tone is detected for each frame of a video signal and a gain is applied to a part of the video signal with a high tone for expanding when the maximum value has a low level. Further, a minimum value of the tone of the video signal is detected and a compression gain is applied to a part of the video signal with a low tone for reducing when the minimum value is high. Using such the enhancement function allows a signal range of the video signal to be wider so that a contrast feeling of a display image is increased, resulting in improvement in image quality.
For example, Patent Literature 1 discloses a liquid crystal display device for automatically adjusting contrast, along with adjustment of luminance of a backlight, so that contrasting of an image closes to that before the adjustment. The liquid crystal display device is configured to change luminance of an image by turning on/off a light source of a backlight device by an operator so as to allow electricity to be effectively saved, and since an enhancement function works according to the changed luminance to adjust a display image with contrast corresponding to the changed luminance, attain almost the same level of contrast in an image as that before lowering luminance even in the case of lowering luminance of the backlight device.